What jellyfish can teach us about our sleep

The observation of animal species teaches us about the evolution of man. Researchers from the Japanese University of Kyushu used this method: they studied jellyfish to better understand sleep. In their work, published in Science Advancesthey show that the notion of sleep precedes that of the brain, because these living beings do not have it, yet they present states similar to that of sleep in humans.

A video observation of jellyfish

The scientific team is interested in hydra vulgaris, an animal species belonging to the jellyfish family, measuring a few centimeters. These animals do not have a central nervous system or a brain. They have only a diffuse network of nerves, without any centralization. The researchers observed these living beings through cameras in order to identify the slightest of their movements. They noticed that their rhythm is based on 4-hour cycles: an alternation between activity and rest, similar to sleep.

Similar chemical mechanisms

A second part of the study was carried out through molecular and genetic observation. The Japanese research team found that jellyfish are sensitive to melatonin, a molecule used to find sleep or improve its quality: when exposed to it, they sleep longer and more regularly. The inhibitory neurotransmitter GABA, also associated with sleep, significantly increased the rest duration of these animals. On the other hand, dopamine should normally cause awakening, but in these jellyfish, it increased the duration of sleep. “Some mechanisms associated with sleep have been conserved, others have changed with evolution“, suggests Taichi Q. Itoh, lead author of the study.”These experiments provide important evidence that animals acquired sleep-related mechanisms before the development of the central nervous system, says the researcher, and many of these mechanisms have been retained.”